Augmented reality systems and methods with variable focus lens elements

ABSTRACT

An augmented reality display system includes a pair of variable focus lens elements that sandwich a waveguide stack. One of the lens elements is positioned between the waveguide stack and a user&#39;s eye to correct for refractive errors in the focusing of light projected from the waveguide stack to that eye. The lens elements may also be configured to provide appropriate optical power to place displayed virtual content on a desired depth plane. The other lens element is between the ambient environment and the waveguide stack, and is configured to provide optical power to compensate for aberrations in the transmission of ambient light through the waveguide stack and the lens element closest to the eye. In addition, an eye-tracking system monitors the vergence of the user&#39;s eyes and automatically and continuously adjusts the optical powers of the pair of lens elements based on the determined vergence of those eyes.

PRIORITY CLAIM

This application is a continuation of U.S. application Ser. No. 16/664,191 filed on Oct. 25, 2019, entitled “AUGMENTED REALITY SYSTEMS AND METHODS WITH VARIABLE FOCUS LENS ELEMENTS”, which is a continuation of U.S. application Ser. No. 15/481,255 filed on Apr. 6, 2017, entitled “AUGMENTED REALITY SYSTEMS AND METHODS WITH VARIABLE FOCUS LENS ELEMENTS” (now U.S. Ser. No. 10/459,231), which claims the priority benefit of U.S. Provisional Patent Application No. 62/320,375 filed on Apr. 8, 2016, entitled “AUGMENTED REALITY SYSTEMS AND METHODS WITH VARIABLE FOCUS LENS ELEMENTS,” which is incorporated by reference herein in its entirety.

INCORPORATION BY REFERENCE

This application also incorporates by reference the entirety of each of the following patent applications: U.S. application Ser. No. 14/555,585 filed on Nov. 27, 2014; U.S. application Ser. No. 14/690,401 filed on Apr. 18, 2015; U.S. application Ser. No. 14/212,961 filed on Mar. 14, 2014; U.S. application Ser. No. 14/331,218 filed on Jul. 14, 2014; and U.S. application Ser. No. 15/072,290 filed on Mar. 16, 2016.

BACKGROUND Field

The present disclosure relates to optical devices, including augmented reality imaging and visualization systems.

Description of the Related Art

Modern computing and display technologies have facilitated the development of systems for so called “virtual reality” or “augmented reality” experiences, in which digitally reproduced images or portions thereof are presented to a user in a manner wherein they seem to be, or may be perceived as, real. A virtual reality, or “VR”, scenario typically involves the presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or “AR”, scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user. A mixed reality, or “MR”, scenario is a type of AR scenario and typically involves virtual objects that are integrated into, and responsive to, the natural world. For example, an MR scenario may include AR image content that appears to be blocked by or is otherwise perceived to interact with objects in the real world.

Referring to FIG. 1 , an augmented reality scene 10 is depicted. The user of an AR technology sees a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. The user also perceives that he/she “sees” “virtual content” such as a robot statue 40 standing upon the real-world platform 30, and a flying cartoon-like avatar character 50 which seems to be a personification of a bumble bee. These elements 50, 40 are “virtual” in that they do not exist in the real world. Because the human visual perception system is complex, it is challenging to produce AR technology that facilitates a comfortable, natural-feeling, rich presentation of virtual image elements amongst other virtual or real-world imagery elements.

Systems and methods disclosed herein address various challenges related to AR and VR technology.

SUMMARY

In some embodiments, a display system is provided. The display system comprises a head-mountable display configured to project light to a viewer to display image information on one or more depth planes. The display comprises one or more waveguides configured to project the light to the viewer. The one or more waveguides are further configured to transmit light from objects in a surrounding environment to the viewer. The display also comprises a first variable focus lens element between the one or more waveguides and a first eye of the viewer; and a second variable focus lens element between the one or more waveguides and the surrounding environment. An eye tracking system is configured to determine vergence of the viewer's eyes. The display system is configured to correct a refractive error of the user's eyes by adjusting an optical power of the first and second variable focus lens elements based on the determined vergence of the viewer's eyes.

In some other embodiments, a method for displaying image information on a head-mountable display is provided. The method comprises providing the display mounted on a head of a viewer, with the display configured to display image information on one or more depth planes. The display comprises one or more waveguides configured to project light to the viewer to display the image information. The one or more waveguides are further configured to transmit light from objects in a surrounding environment to the viewer. The method further comprises determining a vergence point of eyes of the viewer and correcting a refractive error of an eye of the viewer. The refractive error may be corrected by varying optical power of a first variable focus lens element disposed between the one or more waveguides and an eye of the viewer based on the determined vergence point; and varying optical power of a second variable focus lens element disposed between the one or more waveguides and an environment surrounding the viewer based on the determined vergence point.

Example 1: A display system comprising:

-   -   a head-mountable display configured to project light to a viewer         to display image information on one or more depth planes, the         display comprising:     -   one or more waveguides configured to project the light to the         viewer, wherein the one or more waveguides are further         configured to transmit light from objects in a surrounding         environment to the viewer;     -   a first variable focus lens element between the one or more         waveguides and a first eye of the viewer; and     -   a second variable focus lens element between the one or more         waveguides and the surrounding environment; and     -   an eye tracking system configured to determine vergence of the         viewer's eyes, wherein the display system is configured to         correct a refractive error of the user's eyes by adjusting an         optical power of the first and second variable focus lens         elements based on the determined vergence of the viewer's eyes.

Example 2: The display system of Example 1, wherein the display system is configured to modify the optical power of the first and second variable focus lens elements depending on a depth plane for displaying the image information.

Example 3: The display system of any of Examples 1-2, wherein the display system is configured to adjust an optical power of the second variable focus lens element in response to an optical power of the first variable focus lens element.

Example 4: The display system of any of Examples 1-3, wherein the one or more waveguides are configured to project divergent light to the viewer to display the image information.

Example 5: The display system of any of Example 1-4, wherein each of the one or more waveguides has a fixed optical power.

Example 6: The display system of any of Examples 1-5, further comprising a third variable focus element between the one or more waveguides and a second eye of the viewer.

Example 7: The display system of Example 6, further comprising a fourth variable focus element between the one or more waveguides and the surrounding environment.

Example 8: The display system of any of Examples 6-7, wherein the system is configured to adjust an optical power of the third variable focus lens element to vary the wavefront of the projected light based on the determined vergence.

Example 9: The display system of any of Examples 6-8, wherein the system is configured to adjust an optical power of the fourth variable focus lens element to vary the wavefront of incoming light from the object in the surrounding environment based on the determined vergence.

Example 10: The display system of any of Examples 1-9, wherein eye tracking system comprises one or more cameras.

Example 11: The display system of any of Examples 1-10, wherein an optical power of the first and/or second variable focus lens element is adjusted in accordance with a prescription for correcting the viewer's vision at two or more distances.

Example 12: The display system of any of Examples 1-11, wherein the system has three or more preset prescription optical powers for each of the first and second variable focus lens elements.

Example 13: The display system of any of Examples 1-12, wherein a number of available prescription optical powers is equal to at least a total number of depth planes for the display.

Example 14: The display system of any of Examples 1-13, wherein the first and/or second variable focus lens elements comprises a layer of liquid crystal sandwiched between two substrates.

Example 15: The display system of the Example 14, wherein the first and/or second variable focus lens elements comprise electrodes for altering a refractive index of the liquid crystal layer upon application of a voltage.

Example 16: The display system of Examples 14-15, wherein the substrates comprise glass.

Example 17: The display system of any of Examples 1-16, further comprising an electronic hardware control system configured to vary the refractive index of the first and/or second variable focus lens element by application of an electrical current or voltage.

Example 18: The display system of Example 17, wherein the eye tracking system forms a feedback loop to the electronic hardware control system to vary the refractive index of the first and/or second variable focus lens element in accordance with the determined vergence of the viewer's eyes.

Example 19: A method for displaying image information on a head-mountable display, the method comprising:

-   -   providing the display mounted on a head of a viewer, the display         configured to display image information on one or more depth         planes and comprising:     -   one or more waveguides configured to project light to the viewer         to display the image information,     -   wherein the one or more waveguides are further configured to         transmit light from objects in a surrounding environment to the         viewer;     -   determining a vergence point of eyes of the viewer; and     -   correcting a refractive error of an eye of the viewer by:     -   varying optical power of a first variable focus lens element         disposed between the one or more waveguides and an eye of the         viewer based on the determined vergence point; and     -   varying optical power of a second variable focus lens element         disposed between the one or more waveguides and an environment         surrounding the viewer based on the determined vergence point.

Example 20: The method of Example 19, further comprising:

-   -   a third variable focus lens element and a fourth variable focus         lens element, wherein the third variable focus lens element is         between the one or more waveguides and an other eye of the         viewer, and wherein the fourth variable focus lens element is         directly forward of the third variable focus lens and between         the one or more waveguides and the surrounding environment; and     -   correcting a refractive error of the other eye by varying an         optical power of the third and fourth variable focus lens         elements based on the determined vergence point.

Example 21: The method of Example 20, wherein determining the vergence point comprises tracking a vergence of the eye and the other eye of the viewer using one or more cameras.

Example 22: The method of any of Examples 19-21, wherein the optical power of the first variable focus lens element is varied simultaneously with the optical power of the second variable focus lens element.

Example 23: The method of any of Examples 19-22, wherein the one or more waveguides each comprises diffractive optical elements configured to output divergent light from the waveguides.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a user's view of augmented reality (AR) through an AR device.

FIG. 2 illustrates an example of wearable display system.

FIG. 3 illustrates a conventional display system for simulating three-dimensional imagery for a user.

FIG. 4 illustrates aspects of an approach for simulating three-dimensional imagery using multiple depth planes.

FIGS. 5A-5C illustrate relationships between radius of curvature and focal radius.

FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user.

FIG. 7 illustrates an example of exit beams outputted by a waveguide.

FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes images formed using multiple different component colors.

FIG. 9A illustrates a cross-sectional side view of an example of a set of stacked waveguides that each includes an incoupling optical element.

FIG. 9B illustrates a perspective view of an example of the plurality of stacked waveguides of FIG. 9A.

FIG. 9C illustrates a top-down plan view of an example of the plurality of stacked waveguides of FIGS. 9A and 9B.

FIGS. 10A and 10B are schematic illustrations of examples of displays having variable focus lens elements and one or more waveguides. FIG. 10A shows a waveguide stack with a single waveguide, and FIG. 10B shows a waveguide stack with a plurality of waveguides.

FIG. 11 shows a schematic view of various components of an augmented reality system comprising an eye tracking system.

FIG. 12 depicts an example of a method for varying optical power of variable focus lens elements based on the vergence of a user's eyes.

The drawings are provided to illustrate example embodiments and are not intended to limit the scope of the disclosure.

DETAILED DESCRIPTION

As disclosed herein, augmented reality (AR) systems may display virtual content to a viewer while still allowing the viewer to see the world around them. Preferably, this content is displayed on a head-mountable display, e.g., as part of eyewear, that projects image information to the viewer's eyes, while also transmitting light from the surrounding environment to those eyes, to allow a view of that surrounding environment.

Many viewers, however, have eyes with refractive errors that prevent light from correctly focusing on their eyes' retinas. Examples of refractive errors include myopia, hyperopia, presbyopia, and astigmatism. These viewers may require lens elements with a particular prescription optical power to clearly view the image information projected by the display. In some embodiments, such lens elements may be positioned between a waveguide for projecting the image information and the viewer's eyes. Undesirably, these lens elements and possibly other optically transmissive parts of the display, such as the waveguides, may cause aberrations in the viewer's view of the surrounding environment. In addition, many lens elements have a fixed optical power that may not address all of the refractive errors experienced by a viewer.

In some embodiments, a display system includes first and second variable focus lens elements that sandwich (are positioned on either side of) a waveguide or plurality of waveguides. The first lens element may be between the one or more waveguides and an eye of the viewer, and may be configured to correct for refractive errors in the focusing of light projected from the one or more waveguides to that eye. In addition, in some embodiments, the first lens elements may be configured to provide an appropriate amount of optical power to place displayed virtual content on a desired depth plane. The second lens element may be between the surrounding environment and the one or more waveguides, and may be configured to provide optical power to compensate for aberrations in the transmission of light from the surrounding environment through the waveguides and first lens element. In some embodiments, refractive errors in the viewer's other eye may be separately corrected. For example, a third variable focus lens elements between the other eye and the waveguides, and fourth variable focus lens elements between the waveguides and the surrounding environment may be used to correct for refractive errors in this other eye. The focal length/optical power of the variable focus elements may be varied such that the real world and/or the virtual content are focused on the retina of the user's eye, thereby allowing the user to view both the real and virtual objects with high optical image quality.

In some embodiments, the display is part of a display system that includes an eye tracking system configured to determine the vergence of the viewer's eye. The eye tracking system may be, e.g., one or more cameras that determine the vergence point of the eyes and, as a result, may be utilized to determine the distance at which the eyes are focused, to derive the appropriate correction for the eyes for that distance. It will be appreciated that different corrections may be required for different vergence points, e.g., different corrections may be required for the viewer's eyes to properly focus on near, far, or intermediate objects (whether real or virtual objects). In some embodiments, the ability of the variable focus lens elements to provide variable optical power may allow gradations of correction not readily available for, e.g., prescription eye glasses or contact lenses. For example, two or more, three or more, four or more, or five or more unique corrections (for each eye, in some embodiments) may be available.

Instead of wearing fixed prescription optics, the variable focus lens elements may be configured to provide the desired correction to the user. For example, the augmented reality display system may be configured to provide different optical power for virtual objects projected from different depth planes and/or for real-world objects at different distances. For example, for users requiring near vision correction the variable focus lens elements may be configured to provide a near vision optical power when the user is viewing virtual objects or real-world objects located at distances corresponding to near vision zone. As another example, for users requiring intermediate distance vision correction, the variable focus lens elements may be configured to provide an intermediate distance vision optical power when the user is viewing virtual objects or real-world objects located at distances corresponding to intermediate distance vision zone. As yet another example, for users requiring far vision correction, the variable focus lens elements may be configured to provide a far vision optical power when the user is viewing virtual objects or real-world objects located at distances corresponding to a far vision zone. In some embodiments, a user's prescription for near vision correction, intermediate distance vision correction and far vision correction may be accessed by the display system and the system may vary the optical power of the variable focus lens elements in accordance with the user's prescription when the user is viewing virtual objects or real-world objects located at distances corresponding to the near vision zone, intermediate distance vision zone, and far vision zone.

Advantageously, the first and/or second lens elements may allow the same head-mountable display to be used by a variety of users, without physically changing out corrective lens elements. Rather, the displays adapt to the user. In addition, the variable focus lens elements may be configured to provide the appropriate optical power to place image information projected from the one or more waveguides on a desired depth plane. For example, the variable focus lens elements may be configured to vary the divergence of light projected from the one or more waveguides to the viewer. The adaptability provided by the variable focus lens elements may provide advantages for simplifying the manufacture and design of the display, since the same display may be provided to and used by different users and fewer optical structures may be required to display image information on a range of depth planes. Moreover, the ability to offer a wide range of corrections in real time may allow for a larger number of gradations for correction than readily available with conventional corrective glasses. This may improve the sharpness and/or acuity of the viewer's view of the world and displayed image information, and may also facilitate long-term viewer comfort. In addition, the variable focus lens elements may be configured with different prescriptions by simply changing preset corrections programmed into the display system, thereby allowing the display to readily adapt to new user prescriptions as, e.g., the user ages and the condition of one or both eyes changes.

Reference will now be made to the figures, in which like reference numerals refer to like parts throughout.

FIG. 2 illustrates an example of wearable display system 60. The display system 60 includes a display 70, and various mechanical and electronic modules and systems to support the functioning of that display 70. The display 70 may be coupled to a frame 80, which is wearable by a display system user or viewer 90 and which is configured to position the display 70 in front of the eyes of the user 90. The display 70 may be considered eyewear in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent the ear canal of the user 90 (in some embodiments, another speaker, not shown, may optionally be positioned adjacent the other ear canal of the user to provide stereo/shapeable sound control). The display system may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphone is configured to allow the user to provide inputs or commands to the system 60 (e.g., the selection of voice menu commands, natural language questions, etc.), and/or may allow audio communication with other persons (e.g., with other users of similar display systems. The microphone may further be configured as a peripheral sensor to collect audio data (e.g., sounds from the user and/or environment). In some embodiments, the display system may also include a peripheral sensor 120 a, which may be separate from the frame 80 and attached to the body of the user 90 (e.g., on the head, torso, an extremity, etc. of the user 90). The peripheral sensor 120 a may be configured to acquire data characterizing a physiological state of the user 90 in some embodiments. For example, the sensor 120 a may be an electrode.

With continued reference to FIG. 2 , the display 70 is operatively coupled by communications link 130, such as by a wired lead or wireless connectivity, to a local data processing module 140 which may be mounted in a variety of configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removably attached to the user 90 (e.g., in a backpack-style configuration, in a belt-coupling style configuration). Similarly, the sensor 120 a may be operatively coupled by communications link 120 b, e.g., a wired lead or wireless connectivity, to the local processor and data module 140. The local processing and data module 140 may comprise a hardware processor, as well as digital memory, such as non-volatile memory (e.g., flash memory or hard disk drives), both of which may be utilized to assist in the processing, caching, and storage of data. The data include data a) captured from sensors (which may be, e.g., operatively coupled to the frame 80 or otherwise attached to the user 90), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, gyros, and/or other sensors disclosed herein; and/or b) acquired and/or processed using remote processing module 150 and/or remote data repository 160 (including data relating to virtual content), possibly for passage to the display 70 after such processing or retrieval. The local processing and data module 140 may be operatively coupled by communication links 170, 180, such as via a wired or wireless communication links, to the remote processing module 150 and remote data repository 160 such that these remote modules 150, 160 are operatively coupled to each other and available as resources to the local processing and data module 140. In some embodiments, the local processing and data module 140 may include one or more of the image capture devices, microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, and/or gyros. In some other embodiments, one or more of these sensors may be attached to the frame 80, or may be standalone structures that communicate with the local processing and data module 140 by wired or wireless communication pathways.

With continued reference to FIG. 2 , in some embodiments, the remote processing module 150 may comprise one or more processors configured to analyze and process data and/or image information. In some embodiments, the remote data repository 160 may comprise a digital data storage facility, which may be available through the internet or other networking configuration in a “cloud” resource configuration. In some embodiments, the remote data repository 160 may include one or more remote servers, which provide information, e.g., information for generating augmented reality content, to the local processing and data module 140 and/or the remote processing module 150. In some embodiments, all data is stored and all computations are performed in the local processing and data module, allowing fully autonomous use from a remote module.

With reference now to FIG. 3 , the perception of an image as being “three-dimensional” or “3-D” may be achieved by providing slightly different presentations of the image to each eye of the viewer. FIG. 3 illustrates a conventional display system for simulating three-dimensional imagery for a user. Two distinct images 190, 200—one for each eye 210, 220—are outputted to the user. The images 190, 200 are spaced from the eyes 210, 220 by a distance 230 along an optical or z-axis that is parallel to the line of sight of the viewer. The images 190, 200 are flat and the eyes 210, 220 may focus on the images by assuming a single accommodated state. Such 3-D display systems rely on the human visual system to combine the images 190, 200 to provide a perception of depth and/or scale for the combined image.

It will be appreciated, however, that the human visual system is more complicated and providing a realistic perception of depth is more challenging. For example, many viewers of conventional “3-D” display systems find such systems to be uncomfortable or may not perceive a sense of depth at all. Without being limited by theory, it is believed that viewers of an object may perceive the object as being “three-dimensional” due to a combination of vergence and accommodation. Vergence movements (i.e., rotation of the eyes so that the pupils move toward or away from each other to converge the lines of sight of the eyes to fixate upon an object) of the two eyes relative to each other are closely associated with focusing (or “accommodation”) of the lenses and pupils of the eyes. Under normal conditions, changing the focus of the lenses of the eyes, or accommodating the eyes, to change focus from one object to another object at a different distance will automatically cause a matching change in vergence to the same distance, under a relationship known as the “accommodation-vergence reflex,” as well as pupil dilation or constriction. Likewise, a change in vergence will trigger a matching change in accommodation of lens shape and pupil size, under normal conditions. As noted herein, many stereoscopic or “3-D” display systems display a scene using slightly different presentations (and, so, slightly different images) to each eye such that a three-dimensional perspective is perceived by the human visual system. Such systems are uncomfortable for many viewers, however, since they, among other things, simply provide different presentations of a scene, but with the eyes viewing all the image information at a single accommodated state, and work against the “accommodation-vergence reflex.” Display systems that provide a better match between accommodation and vergence may form more realistic and comfortable simulations of three-dimensional imagery.

FIG. 4 illustrates aspects of an approach for simulating three-dimensional imagery using multiple depth planes. With reference to FIG. 4 , objects at various distances from eyes 210, 220 on the z-axis are accommodated by the eyes 210, 220 so that those objects are in focus. The eyes 210, 220 assume particular accommodated states to bring into focus objects at different distances along the z-axis. Consequently, a particular accommodated state may be said to be associated with a particular one of depth planes 240, with has an associated focal distance, such that objects or parts of objects in a particular depth plane are in focus when the eye is in the accommodated state for that depth plane. In some embodiments, three-dimensional imagery may be simulated by providing different presentations of an image for each of the eyes 210, 220, and also by providing different presentations of the image corresponding to each of the depth planes. While shown as being separate for clarity of illustration, it will be appreciated that the fields of view of the eyes 210, 220 may overlap, for example, as distance along the z-axis increases. In addition, while shown as flat for ease of illustration, it will be appreciated that the contours of a depth plane may be curved in physical space, such that all features in a depth plane are in focus with the eye in a particular accommodated state.

The distance between an object and the eye 210 or 220 may also change the amount of divergence of light from that object, as viewed by that eye. FIGS. 5A-5C illustrate relationships between distance and the divergence of light rays. The distance between the object and the eye 210 is represented by, in order of decreasing distance, R1, R2, and R3. As shown in FIGS. 5A-5C, the light rays become more divergent as distance to the object decreases. As distance increases, the light rays become more collimated. Stated another way, it may be said that the light field produced by a point (the object or a part of the object) has a spherical wavefront curvature, which is a function of how far away the point is from the eye of the user. The curvature increases with decreasing distance between the object and the eye 210. Consequently, at different depth planes, the degree of divergence of light rays is also different, with the degree of divergence increasing with decreasing distance between depth planes and the viewer's eye 210. While only a single eye 210 is illustrated for clarity of illustration in FIGS. 5A-5C and other figures herein, it will be appreciated that the discussions regarding eye 210 may be applied to both eyes 210 and 220 of a viewer.

Without being limited by theory, it is believed that the human eye typically can interpret a finite number of depth planes to provide depth perception. Consequently, a highly believable simulation of perceived depth may be achieved by providing, to the eye, different presentations of an image corresponding to each of these limited number of depth planes. The different presentations may be separately focused by the viewer's eyes, thereby helping to provide the user with depth cues based on the accommodation of the eye required to bring into focus different image features for the scene located on different depth plane and/or based on observing different image features on different depth planes being out of focus.

FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. A display system 250 includes a stack of waveguides, or stacked waveguide assembly, 260 that may be utilized to provide three-dimensional perception to the eye/brain using a plurality of waveguides 270, 280, 290, 300, 310. In some embodiments, the display system 250 is the system 60 of FIG. 2 , with FIG. 6 schematically showing some parts of that system 60 in greater detail. For example, the waveguide assembly 260 may be part of the display 70 of FIG. 2 . It will be appreciated that the display system 250 may be considered a light field display in some embodiments. In addition, the waveguide assembly 260 may also be referred to as an eyepiece.

With continued reference to FIG. 6 , the waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and/or the plurality of lenses 320, 330, 340, 350 may be configured to send image information to the eye with various levels of wavefront curvature or light ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image injection devices 360, 370, 380, 390, 400 may function as a source of light for the waveguides and may be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, each of which may be configured, as described herein, to distribute incoming light across each respective waveguide, for output toward the eye 210. Light exits an output surface 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into a corresponding input surface 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, the each of the input surfaces 460, 470, 480, 490, 500 may be an edge of a corresponding waveguide, or may be part of a major surface of the corresponding waveguide (that is, one of the waveguide surfaces directly facing the world 510 or the viewer's eye 210). In some embodiments, a single beam of light (e.g. a collimated beam) may be injected into each waveguide to output an entire field of cloned collimated beams that are directed toward the eye 210 at particular angles (and amounts of divergence) corresponding to the depth plane associated with a particular waveguide. In some embodiments, a single one of the image injection devices 360, 370, 380, 390, 400 may be associated with and inject light into a plurality (e.g., three) of the waveguides 270, 280, 290, 300, 310.

In some embodiments, the image injection devices 360, 370, 380, 390, 400 are discrete displays that each produce image information for injection into a corresponding waveguide 270, 280, 290, 300, 310, respectively. In some other embodiments, the image injection devices 360, 370, 380, 390, 400 are the output ends of a single multiplexed display which may, e.g., pipe image information via one or more optical conduits (such as fiber optic cables) to each of the image injection devices 360, 370, 380, 390, 400. It will be appreciated that the image information provided by the image injection devices 360, 370, 380, 390, 400 may include light of different wavelengths, or colors (e.g., different component colors, as discussed herein).

In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which comprises a light module 540, which may include a light emitter, such as a light emitting diode (LED). The light from the light module 540 may be directed to and modified by a light modulator 530, e.g., a spatial light modulator, via a beam splitter 550. The light modulator 530 may be configured to change the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310. Examples of spatial light modulators include liquid crystal displays (LCD) including a liquid crystal on silicon (LCOS) displays. It will be appreciated that the image injection devices 360, 370, 380, 390, 400 are illustrated schematically and, in some embodiments, these image injection devices may represent different light paths and locations in a common projection system configured to output light into associated ones of the waveguides 270, 280, 290, 300, 310.

In some embodiments, the display system 250 may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous patterns, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the eye 210 of the viewer. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or a plurality of the waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each of which are configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It will be appreciated that one or more optical fibers may be configured to transmit light from the light module 540 to the one or more waveguides 270, 280, 290, 300, 310. It will be appreciated that one or more intervening optical structures may be provided between the scanning fiber, or fibers, and the one or more waveguides 270, 280, 290, 300, 310 to, e.g., redirect light exiting the scanning fiber into the one or more waveguides 270, 280, 290, 300, 310.

A controller 560 controls the operation of one or more of the stacked waveguide assembly 260, including operation of the image injection devices 360, 370, 380, 390, 400, the light source 540, and the light modulator 530. In some embodiments, the controller 560 is part of the local data processing module 140. The controller 560 includes programming (e.g., instructions in a non-transitory medium) that regulates the timing and provision of image information to the waveguides 270, 280, 290, 300, 310 according to, e.g., any of the various schemes disclosed herein. In some embodiments, the controller may be a single integral device, or a distributed system connected by wired or wireless communication channels. The controller 560 may be part of the processing modules 140 or 150 (FIG. 2 ) in some embodiments.

With continued reference to FIG. 6 , the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each respective waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 may each be planar or have another shape (e.g., curved), with major top and bottom surfaces and edges extending between those major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 may each include out-coupling optical elements 570, 580, 590, 600, 610 that are configured to extract light out of a waveguide by redirecting the light, propagating within each respective waveguide, out of the waveguide to output image information to the eye 210. Extracted light may also be referred to as out-coupled light and the out-coupling optical elements light may also be referred to light extracting optical elements. An extracted beam of light may be outputted by the waveguide at locations at which the light propagating in the waveguide strikes a light extracting optical element. The out-coupling optical elements 570, 580, 590, 600, 610 may, for example, be gratings, including diffractive optical features, as discussed further herein. While illustrated disposed at the bottom major surfaces of the waveguides 270, 280, 290, 300, 310, for ease of description and drawing clarity, in some embodiments, the out-coupling optical elements 570, 580, 590, 600, 610 may be disposed at the top and/or bottom major surfaces, and/or may be disposed directly in the volume of the waveguides 270, 280, 290, 300, 310, as discussed further herein. In some embodiments, the out-coupling optical elements 570, 580, 590, 600, 610 may be formed in a layer of material that is attached to a transparent substrate to form the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material and the out-coupling optical elements 570, 580, 590, 600, 610 may be formed on a surface and/or in the interior of that piece of material.

With continued reference to FIG. 6 , as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light to form an image corresponding to a particular depth plane. For example, the waveguide 270 nearest the eye may be configured to deliver collimated light (which was injected into such waveguide 270), to the eye 210. The collimated light may be representative of the optical infinity focal plane. The next waveguide up 280 may be configured to send out collimated light which passes through the first lens 350 (e.g., a negative lens) before it can reach the eye 210; such first lens 350 may be configured to create a slight convex wavefront curvature so that the eye/brain interprets light coming from that next waveguide up 280 as coming from a first focal plane closer inward toward the eye 210 from optical infinity. Similarly, the third up waveguide 290 passes its output light through both the first 350 and second 340 lenses before reaching the eye 210; the combined optical power of the first 350 and second 340 lenses may be configured to create another incremental amount of wavefront curvature so that the eye/brain interprets light coming from the third waveguide 290 as coming from a second focal plane that is even closer inward toward the person from optical infinity than was light from the next waveguide up 280.

The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power representative of the closest focal plane to the person. To compensate for the stack of lenses 320, 330, 340, 350 when viewing/interpreting light coming from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be disposed at the top of the stack to compensate for the aggregate power of the lens stack 320, 330, 340, 350 below. Such a configuration provides as many perceived focal planes as there are available waveguide/lens pairings. Both the out-coupling optical elements of the waveguides and the focusing aspects of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, either or both may be dynamic using electro-active features.

In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same plurality of depth planes, with one set for each depth plane. This can provide advantages for forming a tiled image to provide an expanded field of view at those depth planes.

With continued reference to FIG. 6 , the out-coupling optical elements 570, 580, 590, 600, 610 may be configured to both redirect light out of their respective waveguides and to output this light with the appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides having different associated depth planes may have different configurations of out-coupling optical elements 570, 580, 590, 600, 610, which output light with a different amount of divergence depending on the associated depth plane. In some embodiments, the light extracting optical elements 570, 580, 590, 600, 610 may be volumetric or surface features, which may be configured to output light at specific angles. For example, the light extracting optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and/or diffraction gratings. In some embodiments, the features 320, 330, 340, 350 may not be lenses; rather, they may simply be spacers (e.g., cladding layers and/or structures for forming air gaps).

In some embodiments, the out-coupling optical elements 570, 580, 590, 600, 610 are diffractive features that form a diffraction pattern, or “diffractive optical element” (also referred to herein as a “DOE”). Preferably, the DOE's have a sufficiently low diffraction efficiency so that only a portion of the light of the beam is deflected away toward the eye 210 with each intersection of the DOE, while the rest continues to move through a waveguide via TIR. The light carrying the image information is thus divided into a number of related exit beams that exit the waveguide at a multiplicity of locations and the result is a fairly uniform pattern of exit emission toward the eye 210 for this particular collimated beam bouncing around within a waveguide.

In some embodiments, one or more DOEs may be switchable between “on” states in which they actively diffract, and “off” states in which they do not significantly diffract. For instance, a switchable DOE may comprise a layer of polymer dispersed liquid crystal, in which microdroplets comprise a diffraction pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not appreciably diffract incident light) or the microdroplet may be switched to an index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

In some embodiments, a camera assembly 630 (e.g., a digital camera, including visible light and infrared light cameras) may be provided to capture images of the eye 210 and/or tissue around the eye 210 to, e.g., detect user inputs and/or to monitor the physiological state of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source to project light (e.g., infrared light) to the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be attached to the frame 80 (FIG. 2 ) and may be in electrical communication with the processing modules 140 and/or 150, which may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized for each eye, to separately monitor each eye.

With reference now to FIG. 7 , an example of exit beams outputted by a waveguide is shown. One waveguide is illustrated, but it will be appreciated that other waveguides in the waveguide assembly 260 (FIG. 6 ) may function similarly, where the waveguide assembly 260 includes multiple waveguides. Light 640 is injected into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At points where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as exit beams 650. The exit beams 650 are illustrated as substantially parallel but, as discussed herein, they may also be redirected to propagate to the eye 210 at an angle (e.g., forming divergent exit beams), depending on the depth plane associated with the waveguide 270. It will be appreciated that substantially parallel exit beams may be indicative of a waveguide with out-coupling optical elements that out-couple light to form images that appear to be set on a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of out-coupling optical elements may output an exit beam pattern that is more divergent, which would require the eye 210 to accommodate to a closer distance to bring it into focus on the retina and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

In some embodiments, a full color image may be formed at each depth plane by overlaying images in each of the component colors, e.g., three or more component colors. FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes images formed using multiple different component colors. The illustrated embodiment shows depth planes 240 a-240 f, although more or fewer depths are also contemplated. Each depth plane may have three or more component color images associated with it, including: a first image of a first color, G; a second image of a second color, R; and a third image of a third color, B. Different depth planes are indicated in the figure by different numbers for diopters (dpt) following the letters G, R, and B. Just as examples, the numbers following each of these letters indicate diopters (1/m), or inverse distance of the depth plane from a viewer, and each box in the figures represents an individual component color image. In some embodiments, to account for differences in the eye's focusing of light of different wavelengths, the exact placement of the depth planes for different component colors may vary. For example, different component color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and/or may decrease chromatic aberrations.

In some embodiments, light of each component color may be outputted by a single dedicated waveguide and, consequently, each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figures including the letters G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane where three component color images are provided per depth plane. While the waveguides associated with each depth plane are shown adjacent to one another in this drawing for ease of description, it will be appreciated that, in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple component colors may be outputted by the same waveguide, such that, e.g., only a single waveguide may be provided per depth plane.

With continued reference to FIG. 8 , in some embodiments, G is the color green, R is the color red, and B is the color blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or may replace one or more of red, green, or blue.

It will be appreciated that references to a given color of light throughout this disclosure will be understood to encompass light of one or more wavelengths within a range of wavelengths of light that are perceived by a viewer as being of that given color. For example, red light may include light of one or more wavelengths in the range of about 620-780 nm, green light may include light of one or more wavelengths in the range of about 492-577 nm, and blue light may include light of one or more wavelengths in the range of about 435-493 nm.

In some embodiments, the light source 540 (FIG. 6 ) may be configured to emit light of one or more wavelengths outside the visual perception range of the viewer, for example, infrared and/or ultraviolet wavelengths. In addition, the in-coupling, out-coupling, and other light redirecting structures of the waveguides of the display 250 may be configured to direct and emit this light out of the display towards the user's eye 210, e.g., for imaging and/or user stimulation applications.

With reference now to FIG. 9A, in some embodiments, light impinging on a waveguide may need to be redirected to in-couple that light into the waveguide. An in-coupling optical element may be used to redirect and in-couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 660 of stacked waveguides that each includes an in-coupling optical element. The waveguides may each be configured to output light of one or more different wavelengths, or one or more different ranges of wavelengths. It will be appreciated that the stack 660 may correspond to the stack 260 (FIG. 6 ) and the illustrated waveguides of the stack 660 may correspond to part of the plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more of the image injection devices 360, 370, 380, 390, 400 is injected into the waveguides from a position that requires light to be redirected for in-coupling.

The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated in-coupling optical element (which may also be referred to as a light input area on the waveguide), with, e.g., in-coupling optical element 700 disposed on a major surface (e.g., an upper major surface) of waveguide 670, in-coupling optical element 710 disposed on a major surface (e.g., an upper major surface) of waveguide 680, and in-coupling optical element 720 disposed on a major surface (e.g., an upper major surface) of waveguide 690. In some embodiments, one or more of the in-coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the respective waveguide 670, 680, 690 (particularly where the one or more in-coupling optical elements are reflective, deflecting optical elements). As illustrated, the in-coupling optical elements 700, 710, 720 may be disposed on the upper major surface of their respective waveguide 670, 680, 690 (or the top of the next lower waveguide), particularly where those in-coupling optical elements are transmissive, deflecting optical elements. In some embodiments, the in-coupling optical elements 700, 710, 720 may be disposed in the body of the respective waveguide 670, 680, 690. In some embodiments, as discussed herein, the in-coupling optical elements 700, 710, 720 are wavelength selective, such that they selectively redirect one or more wavelengths of light, while transmitting other wavelengths of light. While illustrated on one side or corner of their respective waveguide 670, 680, 690, it will be appreciated that the in-coupling optical elements 700, 710, 720 may be disposed in other areas of their respective waveguide 670, 680, 690 in some embodiments.

As illustrated, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset such that it receives light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from a different image injection device 360, 370, 380, 390, and 400 as shown in FIG. 6 , and may be separated (e.g., laterally spaced apart) from other in-coupling optical elements 700, 710, 720 such that it substantially does not receive light from the other ones of the in-coupling optical elements 700, 710, 720.

Each waveguide also includes associated light distributing elements, with, e.g., light distributing elements 730 disposed on a major surface (e.g., a top major surface) of waveguide 670, light distributing elements 740 disposed on a major surface (e.g., a top major surface) of waveguide 680, and light distributing elements 750 disposed on a major surface (e.g., a top major surface) of waveguide 690. In some other embodiments, the light distributing elements 730, 740, 750, may be disposed on a bottom major surface of associated waveguides 670, 680, 690, respectively. In some other embodiments, the light distributing elements 730, 740, 750, may be disposed on both top and bottom major surface of associated waveguides 670, 680, 690, respectively; or the light distributing elements 730, 740, 750, may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

The waveguides 670, 680, 690 may be spaced apart and separated by, e.g., gas, liquid, and/or solid layers of material. For example, as illustrated, layer 760 a may separate waveguides 670 and 680; and layer 760 b may separate waveguides 680 and 690. In some embodiments, the layers 760 a and 760 b are formed of low refractive index materials (that is, materials having a lower refractive index than the material forming the immediately adjacent one of waveguides 670, 680, 690). Preferably, the refractive index of the material forming the layers 760 a, 760 b is 0.05 or more, or 0.10 or less than the refractive index of the material forming the waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760 a, 760 b may function as cladding layers that facilitate total internal reflection (TIR) of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760 a, 760 b are formed of air. While not illustrated, it will be appreciated that the top and bottom of the illustrated set 660 of waveguides may include immediately neighboring cladding layers.

Preferably, for ease of manufacturing and other considerations, the material forming the waveguides 670, 680, 690 are similar or the same, and the material forming the layers 760 a, 760 b are similar or the same. In some embodiments, the material forming the waveguides 670, 680, 690 may be different between one or more waveguides, and/or the material forming the layers 760 a, 760 b may be different, while still holding to the various refractive index relationships noted above.

With continued reference to FIG. 9A, light rays 770, 780, 790 are incident on the set 660 of waveguides. It will be appreciated that the light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6 ).

In some embodiments, the light rays 770, 780, 790 have different properties, e.g., different wavelengths or different ranges of wavelengths, which may correspond to different colors. The in-coupling optical elements 700, 710, 720 each deflect the incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, the incoupling optical elements 700, 710, 720 each selectively deflect one or more particular wavelengths of light, while transmitting other wavelengths to an underlying waveguide and associated incoupling optical element.

For example, in-coupling optical element 700 may be configured to deflect ray 770, which has a first wavelength or range of wavelengths, while transmitting rays 780 and 790, which have different second and third wavelengths or ranges of wavelengths, respectively. The transmitted ray 780 impinges on and is deflected by the in-coupling optical element 710, which is configured to deflect light of a second wavelength or range of wavelengths. The ray 790 is deflected by the in-coupling optical element 720, which is configured to selectively deflect light of third wavelength or range of wavelengths.

With continued reference to FIG. 9A, the deflected light rays 770, 780, 790 are deflected so that they propagate through a corresponding waveguide 670, 680, 690; that is, the in-coupling optical elements 700, 710, 720 of each waveguide deflects light into that corresponding waveguide 670, 680, 690 to in-couple light into that corresponding waveguide. The light rays 770, 780, 790 are deflected at angles that cause the light to propagate through the respective waveguide 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguide 670, 680, 690 by TIR until impinging on the waveguide's corresponding light distributing elements 730, 740, 750.

With reference now to FIG. 9B, a perspective view of an example of the plurality of stacked waveguides of FIG. 9A is illustrated. As noted above, the in-coupled light rays 770, 780, 790, are deflected by the in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within the waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then impinge on the light distributing elements 730, 740, 750, respectively. The light distributing elements 730, 740, 750 deflect the light rays 770, 780, 790 so that they propagate towards the out-coupling optical elements 800, 810, 820, respectively.

In some embodiments, the light distributing elements 730, 740, 750 are orthogonal pupil expanders (OPE's). In some embodiments, the OPE's deflect or distribute light to the out-coupling optical elements 800, 810, 820 and, in some embodiments, may also increase the beam or spot size of this light as it propagates to the out-coupling optical elements. In some embodiments, the light distributing elements 730, 740, 750 may be omitted and the in-coupling optical elements 700, 710, 720 may be configured to deflect light directly to the out-coupling optical elements 800, 810, 820. For example, with reference to FIG. 9A, the light distributing elements 730, 740, 750 may be replaced with out-coupling optical elements 800, 810, 820, respectively. In some embodiments, the out-coupling optical elements 800, 810, 820 are exit pupils (EP's) or exit pupil expanders (EPE's) that direct light in a viewer's eye 210 (FIG. 7 ). It will be appreciated that the OPE's may be configured to increase the dimensions of the eye box in at least one axis and the EPE's may be to increase the eye box in an axis crossing, e.g., orthogonal to, the axis of the OPEs. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE of the same waveguide, while allowing the remaining portion of the light to continue to propagate down the waveguide. Upon impinging on the OPE again, another portion of the remaining light is redirected to the EPE, and the remaining portion of that portion continues to propagate further down the waveguide, and so on. Similarly, upon striking the EPE, a portion of the impinging light is directed out of the waveguide towards the user, and a remaining portion of that light continues to propagate through the waveguide until it strikes the EP again, at which time another portion of the impinging light is directed out of the waveguide, and so on. Consequently, a single beam of incoupled light may be “replicated” each time a portion of that light is redirected by an OPE or EPE, thereby forming a field of cloned beams of light, as shown in FIG. 6 . In some embodiments, the OPE and/or EPE may be configured to modify a size of the beams of light.

Accordingly, with reference to FIGS. 9A and 9B, in some embodiments, the set 660 of waveguides includes waveguides 670, 680, 690; in-coupling optical elements 700, 710, 720; light distributing elements (e.g., OPE's) 730, 740, 750; and out-coupling optical elements (e.g., EP's) 800, 810, 820 for each component color. The waveguides 670, 680, 690 may be stacked with an air gap/cladding layer between each one. The in-coupling optical elements 700, 710, 720 redirect or deflect incident light (with different in-coupling optical elements receiving light of different wavelengths) into its waveguide. The light then propagates at an angle which will result in TIR within the respective waveguide 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700, and then continues to bounce down the waveguide, interacting with the light distributing element (e.g., OPE's) 730 and then the out-coupling optical element (e.g., EPs) 800, in a manner described earlier. The light rays 780 and 790 (e.g., green and red light, respectively) will pass through the waveguide 670, with light ray 780 impinging on and being deflected by in-coupling optical element 710. The light ray 780 then bounces down the waveguide 680 via TIR, proceeding on to its light distributing element (e.g., OPEs) 740 and then the out-coupling optical element (e.g., EP's) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 to impinge on the light in-coupling optical elements 720 of the waveguide 690. The light in-coupling optical elements 720 deflect the light ray 790 such that the light ray propagates to light distributing element (e.g., OPEs) 750 by TIR, and then to the out-coupling optical element (e.g., EPs) 820 by TIR. The out-coupling optical element 820 then finally out-couples the light ray 790 to the viewer, who also receives the out-coupled light from the other waveguides 670, 680.

FIG. 9C illustrates a top-down plan view of an example of the plurality of stacked waveguides of FIGS. 9A and 9B. As illustrated, the waveguides 670, 680, 690, along with each waveguide's associated light distributing element 730, 740, 750 and associated out-coupling optical element 800, 810, 820, may be vertically aligned. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned; rather, the in-coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart as seen in the top-down view). As discussed further herein, this nonoverlapping spatial arrangement facilitates the injection of light from different resources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, arrangements including nonoverlapping spatially-separated in-coupling optical elements may be referred to as a shifted pupil system, and the in-coupling optical elements within these arrangements may correspond to sub pupils.

Reference will now be made to FIGS. 10A and 10B. Some embodiments of augmented reality devices, such as those described above, may be configured to adjust the wavefront of light (including light for image information projected from the augmented reality system as well as incoming light from objects in the surrounding real world) by tuning focal lengths of variable focus lens elements included in the augmented reality system. As discussed above, the augmented reality system may comprise a display device that may include a plurality of stacked waveguides (e.g., corresponding to the plurality or set 660 of stacked waveguides of FIGS. 9A and 9B, or corresponding to the stacked waveguide assembly 260 of FIG. 6 ) that project light towards the eyes of a user or a viewer (e.g., the viewer or user 90 of FIG. 2 ). In some other embodiments, the display device may include only a single waveguide. Consequently, while plural waveguides are referenced in various parts of the disclosure herein, it will be appreciated that the plural waveguides may be replaced by a singular waveguide.

As discussed herein, the projected light from the waveguides may be used to provide virtual, augmented reality image information to the viewer. The light may be projected such that the user perceives the light to originate from one or more different depths, or distances from the viewer. The display device may be optically transmissive, such that the user can see real-world objects in the surrounding environment through the display device. In some embodiments, the waveguides may be configured to have fixed optical power. To provide the appearance that the projected light is originating from different depths, the waveguides may be configured to output divergent beams of light, with different amounts of divergence corresponding to different depth planes.

It will be appreciated that the fixed optical power of the waveguides assumes that the viewer's eyes have a suitable accommodative range to focus the light outputted by the waveguides. As discussed above, however, some viewers may require corrective lens to see clearly and, as a result, the image information outputted from a waveguide may not be clearly seen by such viewers. In some embodiments, a first variable focus lens element may be provided between the waveguide and the viewer's eye to provide an appropriate adjustment to the wavefront of the light outputted by the waveguide, to allow this light to be correctly focused by the viewer's eye. This first lens element, however, is also in the path of light propagating from the surrounding environment to the viewer's eye. As a result, the first lens element may modify the wavefront of the light from the surrounding environment and, thereby cause aberrations in the viewer's view of the world. To correct such aberrations, a second variable focus lens element may be disposed on the opposite side of the plurality of stacked waveguides from the first variable focus lens element; that is, the second variable focus lens element may be between the plurality of stacked waveguides and the surrounding real world to adjust the wavefront of light from real-world objects in the surrounding environment. The second variable focus lens element may be configured to compensate for aberrations caused by the first variable focus lens element. In some embodiments, the second variable focus lens may also be configured to compensate for aberrations caused by the waveguides.

In some embodiments, the focus of the second variable focus lens element may be inverse or opposite the focus of the first variable focus lens element. For example, if the first variable focus lens element has a positive optical power, then the second variable focus lens element may have a negative optical power, which may be of similar magnitude. In some other embodiments, to compensate for both the optical power of the first variable focus lens element and the optical power of the intervening waveguides, the optical power of the second lens elements may be opposite to and of similar magnitude as the aggregate optical power of the first lens element and the waveguides.

In some other embodiments, the waveguides may not have optical power (e.g., the waveguides may be configured to output collimated light), and the first variable focus lens elements may be configured to modify the wavefront of light emitted from the waveguides to provide the appropriate amount of divergence for image information to be interpreted by the viewer as being on a particular depth plane. It will be appreciated that the appropriate amount of divergence may vary for different viewers since optical power for placing image information on a particular depth plane will be adjusted by a particular differential to account for a viewer's optical prescription for that depth plane. In such embodiments, the waveguide stack between the first and second variable focus lens elements may simply be formed by a single waveguide.

It will be appreciated that the first and second variable focus lens elements may be provided for one of the viewer's eyes, and that third and fourth variable focus lens elements that are similar to the first and second variable focus lens elements, respectively, may be provided for the other of the viewer's eyes.

FIGS. 10A and 10B show schematic illustrations of examples of display systems (e.g., augmented reality display systems) having variable focus lens elements and a waveguide stack. It will be appreciated that the display system 2010 may correspond to the display system 250 (FIG. 6 ). The example display system 2010 of FIG. 10A shows a waveguide stack with a single waveguide, while the example of FIG. 10B shows a waveguide stack with a plurality of waveguides. In both FIGS. 10A and 10B, a first variable focus lens element 2007 a and a second variable focus lens element 2007 b are disposed on either side of a waveguide stack 2005 (FIG. 10A), and a third variable focus lens element 2008 a and a fourth variable focus lens element 2008 b are disposed on either side of a waveguide stack 2006 (FIG. 10B).

The various illustrated waveguides 2005 a, 2005 b, 2006 a, 2006 b of FIGS. 10A and 10B may have characteristics and/or features similar to individual ones of waveguides 270, 280, 290, 300, 310 of FIG. 6 and/or waveguides 670, 680, and 690 of FIGS. 9A and 9B. The waveguide stacks 2005, 2006 may have characteristics and/or features similar to the plurality or set 660 of stacked waveguides of FIGS. 9A and 9B or to the stacked waveguide assembly 260 of FIG. 6 . In some embodiments, the waveguides 2005 a, 2005 b, 2006 a, 2006 b may include optical elements, such as diffractive optical elements, that provide the waveguides with optical power, e.g., a fixed optical power. For example, one or more of these waveguides may have an optical power in the range between 0 Diopter and about 5.0 Diopters, between about 0.5 Diopters and about 4.5 Diopters, between about 1.0 Diopters and about 4.0 Diopters, between about 1.5 Diopters and about 3.5 Diopters, between about 2.0 Diopters and about 3.0 Diopters, or any value in these ranges or sub-ranges. As another example, in a particular embodiment, each of the waveguides may have an optical power of 1.5 Diopters.

As discussed above, light providing image information (e.g., virtual content) from an optical source 2003 or 2004 may be injected into the waveguide 2005 a or 2006 a, respectively, such that the light propagates through each of those waveguides by total internal reflection. The propagating light may be projected out of the waveguide 2005 a (or waveguide 2005 b) by out-coupling elements (e.g., corresponding to out-coupling elements 800, 810, 820 of FIGS. 9A and 9B) towards the user's eye 2001. In some embodiments, the optical sources 2003, 2004 may be fiber scanning devices (FSD) that utilize a moving fiber to create a 2D image pattern, as disclosed herein. The FSD may create the 2D image pattern by projecting light in a variety of patterns, such as, for example, raster scan, spiral scan, Lissajous, etc. In some other embodiments, the optical source 2003 a (and/or 2003 b) may be an image projection system, e.g. in which a full image is projected onto a waveguide, as also disclosed herein. It will be appreciated that light from the optical source 2003 a (and/or 2003 b) may be injected into the waveguide stack 2005 through edges of the waveguides or through a major surface of the waveguide. Where the waveguide stack includes a plurality of waveguides, the optical source 2003 and/or 2004 may be configured to inject light into multiple ones of these waveguides, or additional optical sources, e.g., one optical source for each waveguide, may be provided.

As illustrated in FIGS. 10A and 10B, the first variable focus lens element 2007 a may be disposed between the waveguide stack 2005 and the user's eye 2001, and the second variable focus lens element 2007 b may be disposed between the waveguide stack 2005 and the real world surrounding the user. It will be appreciated that the eye 2001 may correspond to the viewer's eye 210 of FIG. 6 . Similarly, the third variable focus lens element 2008 a may be disposed between the waveguide stack 2006 and the user's eye 2002 and the second variable focus lens element 2008 b may be disposed between the waveguide stack 2006 and the real world surrounding the user.

In some embodiments, the first and the second variable focus lens elements 2007 a and 2007 b, and third and fourth variable focus lens elements 2008 a and 2008 b, may be adaptable optical elements. The adaptable optical elements may be dynamically altered, for example, by applying an electrical signal thereto, to change the shape of a wavefront that is incident thereon. In some embodiments, the adaptable optical elements may comprise a transmissive optical element such as a dynamic lens (e.g., a liquid crystal lens, an electro-active lens, a conventional refractive lens with moving elements, a mechanical-deformation-based lens, an electrowetting lens, an elastomeric lens, or a plurality of fluids with different refractive indices). By altering the adaptable optics' shape, refractive index, or other characteristics, the wavefront incident thereon may be changed, for example, to alter the focus of the light by the viewer's eyes, as described herein.

In some embodiments, the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may comprise a layer of liquid crystal sandwiched between two substrates. The substrates may comprise an optically transmissive material such as, for example, glass, plastic, acrylic, etc. In some embodiments, the substrates may be flat. In some embodiments, the substrates may have curved regions such that portions of the substrates may have fixed optical power.

In some embodiments, the optical power of the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may be varied by adjusting an electrical signal (e.g., current and/or voltage) applied to the liquid crystal layer via, e.g., one or more thin film transistors (TFTs) and/or electrodes integrated with the liquid crystal layer and/or the substrates. It will be appreciated that the orientations of liquid crystal species in the liquid crystal layer determines the refractive index of the layer. The applied electrical signal sets the orientation of the liquid crystal species, thereby allowing the refractive index of the liquid crystal layer to be varied as desired by altering the applied electrical signal. In some embodiments, the optical power of the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may be varied between about ±5.0 Diopters (e.g., between about −4.0 Diopters and +4.0 Diopters; between about −3.5 Diopters and about +3.5 Diopters, between about −3.0 Diopters and about +3.0 Diopters, between about −2.0 Diopters and about +2.0 Diopters, between about −1.5 Diopters and about +1.5 Diopters, including values in any of these ranges or sub-ranges).

Advantageously, the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may have a wide aperture that is substantially matched to the aperture of the waveguides of their respective associated waveguide stacks 2005, 2006. In some embodiments, the apertures of the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may be substantially equal (e.g., within about ±20%, about ±15%, or about ±10%) to the surface areas of the waveguides of the waveguide stacks 2005, 2006. Consequently, the areas over which the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b and the waveguide stacks 2005, 2206 transmit light to an associated eye 2001, 2002 may be substantially equal.

With continued reference to FIGS. 10A and 10B, the first and third variable focus lens elements 2007 a, 2008 a may each have its optical power varied to adjust the wavefront of light projected from a waveguide of the waveguide stacks 2005, 2006, respectively, to properly focus that light onto the retina of the eyes 2001, 2002, respectively. As noted herein, the first and third variable focus lens elements 2007 a, 2008 a may cause aberrations in the wavefront of incoming light from an object 2009 in the surrounding environment, thereby diminishing the optical image quality of real-world objects 2009 viewed through the first variable focus lens element 2007 a. The second and fourth variable focus lens elements 2007 b, 2008 b may advantageously compensate for the aberrations introduced by the first and third variable focus lens elements 2007 a, 2008 a, respectively, and any waveguides when viewing the object 2009. In some embodiments, the second and fourth variable focus lens elements 2007 b, 2008 b may be configured to provide an optical power opposite to the optical power provided by the first and third variable focus lens elements 2007 a, 2008 a, respectively, and the associated waveguide stack 2005, 2006. In some embodiments, the magnitude of the opposite optical power is such that the net optical power of the display system 2010, for each eye 2001, 2002, is equal to an optical prescription for the eye at the depth plane that the eye is verging towards. The optical power provided by the first and the second variable focus lens elements 2007 a and 2007 b may be varied and controlled by an electronic hardware control system 2011. In some embodiments, the electronic hardware control system 2011 may correspond to the local processing and data module 140 and/or the remote processing module 150 of FIG. 2 .

In some embodiments, the augmented reality display system 2010 may be configured to determine vergence of the user's eyes. The optical power of the first and the second variable focus lens elements 2007 a, 2007 b may be set based upon the vergence point of the eyes 2001, 2002. The optical power of the third and the fourth variable focus lens elements 2008 a, 2008 b may also be set based upon this vergence point. It will be appreciated that the vergence point is the point in space at which the lines of sight of the eyes 2001, 2002 converge and may correspond to the physiologic accommodation target of those eyes. In some embodiments, the distance that the point is away from the eyes 2001, 2002 may be calculated based, e.g., on the known quantities of the separation between the eyes 2001, 2002 and the angles made out by the each eye. Once that distance is calculated, an appropriate correction for the viewer for that distance may be determined. For example, the display system 2010 may be programmed with one or more optical prescriptions. In some embodiments, the optical prescriptions may be stored in the local processing and data module 140 and/or the remote data repository 160. The distance between the eyes 2001, 2002 and the vergence point may be matched with the appropriate correction for that distance, and the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may be adjusted to provide the correction. In some embodiments, the eyes 2001, 2002 may have different prescribed corrections and, as a result, the pairs of variable focus lens elements 2007 a, 2007 b, and 2008 a, 2008 b, may provide different optical power.

Advantageously, the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b provide for a large number of possible corrections since their optical power can be adjusted as desired by, e.g., the application of different voltages. In some embodiments, the total number of corrections per eye may be 1, 2, 3, or 4 more. In some embodiments, the total number of corrections per eye may be equal to the number of depth planes that the display system 2010 is configured to display image information on. It will be appreciated that these corrections may correspond to optical prescriptions, which may be determined for objects at various distances from the eyes 2001, 2002. For example, four prescriptions may be obtained by determining corrections for refractive errors at four progressively farther distances (e.g., close, close intermediate, far intermediate, and far distances) from the eyes 2001, 2002. In some embodiments, the number of possible corrections for viewing image content outputted by the waveguide stack 2005 may be different from the number of possible corrections when viewing objects 2009 in the surrounding environment.

With continued reference to FIGS. 10A and 10B, in some embodiments, the focus, or optical power, of the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may each be set based upon the determined vergence of the user's eyes 2001, 2004. For example, the optical power of the first and the second variable focus lens elements 2007 a and 2007 b may be varied based on the vergence of the user's eyes 2001 without specific reference to the optical power of the other lens element.

In some embodiments, one of the first and the second variable focus lens elements 2007 a, 2007 b, or one of the third and the fourth variable focus elements 2008 a, 2008 b, may be designated as a master and the other of the first and the second variable focus lens elements 2007 a, 2007 b, or the third and the fourth variable focus elements 2008 a, 2008 b, may be designated as a slave. The variable focus lens element designated as the slave may be configured to follow the master variable focus lens element. In some other embodiments, the second and the fourth variable focus lens elements 2007 b, 2008 b may be slaved to the first and third variable focus lens elements 2007 a, 2008 a, and the focus of the first and third variable focus lens elements 2007 a, 2008 a may be set based upon the determined vergence point of the user's eyes 2001, 2002. For example, if the waveguide 2005 a (and/or waveguide 2005 b) has an optical power of about 1.5 Diopters and the user is verging at 2.0 Diopters, the first variable focus lens element 2007 a may have an optical power of +0.5 Diopters and the second variable focus lens element 2007 b may have an optical power −0.5 Diopters.

The optical powers of the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may be varied in real time, and may preferably be changed at a rate equal to or greater than the rate at which the human eye changes accommodation states. Preferably, the first and second variable focus lens elements can change their optical power before the human eye changes accommodation states, such that the user does not experience a delay in receiving the appropriate correction for a given vergence point. In some embodiments, the first and second variable focus lens elements can change in optical power in less than about 300 ms, less than about 275 ms, or less than about 250 ms. The electronic hardware control system 2011 may drive the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b such that the optical powers of the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b may be varied simultaneously.

Various embodiments of the augmented reality display systems described herein may include an eye tracking system comprising one or more eye tracking cameras or imaging systems to track one or more eyes of the user to determine/measure the vergence of the user's eyes. An example embodiment of an augmented reality system 2010 including an eye tracking system 22 is illustrated in FIG. 11 . The eye tracking system 22 may include cameras 24 (e.g., infrared cameras) paired with light sources 26 (e.g., infrared light sources) directed at and configured to monitor and track the eyes 2001, 2002 of the user. These cameras 24 and light sources 26 may be operatively coupled to the local processing module 140. Such cameras 24 may monitor one or more of the orientations, pupil sizes, and the corresponding direction of the line of sight of the respective eyes. As described herein, the cameras 24 may be configured to determine the vergence point of the eyes 2001, 2002.

With continued reference to FIG. 11 , the cameras 24 and light sources 26 may be mounted on the frame 80, which may also hold the waveguide stacks 2005, 2006. In some embodiments, the cameras 24 may communicate with the local processing and data module 140 through communication links 170, 180.

In some embodiments, in addition to determining the vergence of the eyes 2001, 2002, the cameras 24 may be utilized to track the eyes to provide user input. For example, the eye-tracking system 22 may be utilized to select items on virtual menus, and/or provide other input to the display system 2010.

With reference now to FIG. 12A, a flowchart 2200 is provided depicting an example method of varying the optical power of variable focus lens elements based on the determined vergence of a user. At block 2205, the vergence point of the user's eyes may be determined or measured. Such a determination may be made using, e.g., the eye-tracking systems described herein. Based on this determination, the distance and/or depth plane at which the user's eyes are directed may be estimated. The optical power of a pair of variable lens elements may be varied in accordance with the determined vergence to improve the image quality of the virtual objects and/or real-world objects viewed by the user. At block 2215, the optical power of a variable focus lens element (e.g., one of the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b) is varied to adjust a wavefront of light projected from a waveguide, such as a waveguide of the waveguide stacks 2005, 2006 (FIGS. 10A and 10B). At block 2220, the optical power of another variable focus lens element (e.g., a different one of the variable focus lens elements 2007 a, 2007 b, 2008 a, 2008 b) is varied to adjust a wavefront of incoming ambient light from an object in the surrounding environment. It will be appreciated that blocks 2215, 2220 may be performed sequentially (e.g., with 2215 performed before 2220, or vice versa), or these blocks 2215, 2220 may be performed concurrently. In some embodiments, blocks 2205, 2215, 2220 may be performed continuously by the display system 2010 to automatically and continuously adjust the optical powers of the variable focus lens elements to provide a comfortable viewing experience for the user.

It will be appreciated that each of the processes, methods, and algorithms described herein and/or depicted in the figures may be embodied in, and fully or partially automated by, code modules executed by one or more physical computing systems, hardware computer processors, application-specific circuitry, and/or electronic hardware configured to execute specific and particular computer instructions. For example, computing systems may include general purpose computers (e.g., servers) programmed with specific computer instructions or special purpose computers, special purpose circuitry, and so forth. A code module may be compiled and linked into an executable program, installed in a dynamic link library, or may be written in an interpreted programming language. In some embodiments, particular operations and methods may be performed by circuitry that is specific to a given function.

Further, certain embodiments of the functionality of the present disclosure are sufficiently mathematically, computationally, or technically complex that application-specific hardware or one or more physical computing devices (utilizing appropriate specialized executable instructions) may be necessary to perform the functionality, for example, due to the volume or complexity of the calculations involved or to provide results substantially in real-time. For example, a video may include many frames, with each frame having millions of pixels, and specifically programmed computer hardware is necessary to process the video data to provide a desired image processing task or application in a commercially reasonable amount of time.

Code modules or any type of data may be stored on any type of non-transitory computer-readable medium, such as physical computer storage including hard drives, solid state memory, random access memory (RAM), read only memory (ROM), optical disc, volatile or non-volatile storage, combinations of the same and/or the like. In some embodiments, the non-transitory computer-readable medium may be part of one or more of the local processing and data module (140), the remote processing module (150), and remote data repository (160). The methods and modules (or data) may also be transmitted as generated data signals (e.g., as part of a carrier wave or other analog or digital propagated signal) on a variety of computer-readable transmission mediums, including wireless-based and wired/cable-based mediums, and may take a variety of forms (e.g., as part of a single or multiplexed analog signal, or as multiple discrete digital packets or frames). The results of the disclosed processes or process steps may be stored, persistently or otherwise, in any type of non-transitory, tangible computer storage or may be communicated via a computer-readable transmission medium.

Any processes, blocks, states, steps, or functionalities in flow diagrams described herein and/or depicted in the attached figures should be understood as potentially representing code modules, segments, or portions of code which include one or more executable instructions for implementing specific functions (e.g., logical or arithmetical) or steps in the process. The various processes, blocks, states, steps, or functionalities may be combined, rearranged, added to, deleted from, modified, or otherwise changed from the illustrative examples provided herein. In some embodiments, additional or different computing systems or code modules may perform some or all of the functionalities described herein. The methods and processes described herein are also not limited to any particular sequence, and the blocks, steps, or states relating thereto may be performed in other sequences that are appropriate, for example, in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. Moreover, the separation of various system components in the embodiments described herein is for illustrative purposes and should not be understood as requiring such separation in all embodiments. It should be understood that the described program components, methods, and systems may generally be integrated together in a single computer product or packaged into multiple computer products.

In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.

Indeed, it will be appreciated that the systems and methods of the disclosure each have several innovative aspects, no single one of which is solely responsible or required for the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure.

Certain features that are described in this specification in the context of separate embodiments also may be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment also may be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination may in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. No single feature or group of features is necessary or indispensable to each and every embodiment.

It will be appreciated that conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment. The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. In addition, the articles “a,” “an,” and “the” as used in this application and the appended claims are to be construed to mean “one or more” or “at least one” unless specified otherwise. Similarly, while operations may be depicted in the drawings in a particular order, it is to be recognized that such operations need not be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one more example processes in the form of a flowchart. However, other operations that are not depicted may be incorporated in the example methods and processes that are schematically illustrated. For example, one or more additional operations may be performed before, after, simultaneously, or between any of the illustrated operations. Additionally, the operations may be rearranged or reordered in other embodiments. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

Accordingly, the claims are not intended to be limited to the embodiments shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein. 

What is claimed is:
 1. A display system comprising: a head-mountable display configured to display a virtual object on one or more depth planes, the display comprising: a first variable focus lens element; a second variable focus lens element; one or more waveguides between the first variable focus lens element and the second variable focus lens element, wherein the one or more waveguides are configured to: output light for forming the virtual object, and transmit light from a surrounding environment through the one or more waveguides; and an eye tracking system, wherein the display system is configured to: determine eye parameters indicative of a vergence of a viewer's eyes; and cause the second variable focus lens element to modify a wavefront divergence of the light outputted from the one or more waveguides to display the virtual object on a depth plane, wherein an amount of the modification of the wavefront divergence is based on the eye parameters indicative of the vergence and on an amount to correct a refractive error of a first eye of the viewer.
 2. The display system of claim 1, wherein the system is further configured to project another virtual object to the viewer via the one or more waveguides, wherein the another virtual object is disposed on a different depth plane than the virtual object, and wherein the amount of modification of wavefront divergence is based on the depth plane of the virtual object when a determined depth of the vergence of the viewer's eyes corresponds to the depth plane of the virtual object and the amount of modification of the wavefront divergence is based on the depth plane of the another virtual object when the determined depth of the vergence of the viewer's eyes corresponds to the depth plane of the another virtual object, wherein the amounts of modification for the virtual object and for the other virtual object are different.
 3. The display system of claim 1, wherein the display system is configured to cause the first variable focus lens element to modify a wavefront divergence of incoming light from the surrounding environment, wherein an amount of the modification of the wavefront divergence modified by the first variable focus lens element is based on the determined eye parameters indicative of the vergence of the viewer's eyes and on an amount to correct the refractive error of the viewer's first eye.
 4. The display system of claim 1 wherein the display system is configured to adjust the amount of corrected refractive error of the first variable focus lens element in response to the amount of corrected refractive error of the second variable focus lens element.
 5. The display system of claim 1, wherein the one or more waveguides are configured to output light with a divergent wavefront to the viewer to display the virtual object.
 6. The display system of claim 1, wherein the one or more waveguides comprises a plurality of waveguides each having a fixed optical power.
 7. The display system of claim 6, wherein at least some of the waveguides have different optical powers than others of the waveguides.
 8. The display system of claim 1, further comprising: a third variable focus lens element; a fourth variable focus lens element; and one or more second waveguides between the third variable focus lens element and the fourth variable focus lens element, wherein the one or more second waveguides are configured to: output light for forming the virtual object in a second eye of the viewer, and transmit light from the surrounding environment through the one or more second waveguides.
 9. The display system of claim 8, wherein the display system is configured to cause the fourth variable focus lens element to modify a wavefront divergence of the outputted light for forming the virtual object on a depth plane, wherein an amount of the modification of the wavefront divergence is based on the eye parameters and on an amount to correct a refractive error of the second eye of the viewer.
 10. The display system of claim 9, wherein the display system is configured to cause the third variable focus lens element to modify a wavefront divergence of incoming light from the surrounding environment, wherein an amount of the modification of the wavefront divergence of incoming light is based on the determined eye parameters indicative of the vergence of the viewer's eyes and on an amount to correct the refractive error of the viewer's second eye.
 11. The display system of claim 1, wherein the amount to correct refractive error is adjusted in accordance with a prescription for correcting the vision of the viewer's first eye at two or more distances.
 12. The display system of claim 1, wherein the display system has three or more preset prescriptions for refractive errors for each of the first and second variable focus lens elements.
 13. The display system of claim 1, wherein a number of available refractive error prescriptions is equal to at least a total number of depth planes for the display.
 14. The display system of claim 1, wherein one or both of the first and second variable focus lens elements comprises a layer of liquid crystal sandwiched between two substrates.
 15. The display system of claim 14, further comprising an electronic hardware control system configured to vary the refractive index of the first and/or second variable focus lens element by application of an electrical current or voltage.
 16. A method for displaying images on a head-mountable display, the method comprising: providing the display mounted on a head of a viewer, the display configured to display a virtual object on one or more depth planes and comprising: a first variable focus lens element facing a surrounding environment; a second variable focus lens element facing the viewer; and one or more waveguides between the first variable focus lens element and the second variable focus lens element, wherein the one or more waveguides are configured to: output light for forming the virtual object, and transmit light from a surrounding environment to the viewer; determining eye parameters indicative of a vergence of the viewer's eyes; and correcting a refractive error of a first eye of the viewer by: varying optical power of the second variable focus lens element, wherein the second variable focus lens element modifies a wavefront divergence of the outputted light for forming the virtual object on a depth plane, wherein an amount of the modification of the wavefront divergence is based on the eye parameters indicative of the vergence of the viewer's eyes and on an amount to correct the refractive error of the first eye; and varying optical power of the first variable focus lens element, wherein the optical power of the first variable focus lens element modifies a wavefront divergence of incoming light from the surrounding environment, wherein an amount of the modification of the wavefront divergence of the incoming light is based on the eye parameters indicative of the vergence of the viewer's eyes and on an amount to correct the refractive error of the first eye.
 17. The method of claim 16, further comprising: providing: a third variable focus lens element; a fourth variable focus lens element; and one or more second waveguides between the third variable focus lens element and the fourth variable focus lens element; and correcting a refractive error of a second eye of the viewer by: varying an optical power of the fourth variable focus lens element, wherein the fourth variable focus lens element modifies a wavefront divergence of the outputted light for forming the virtual object on the depth plane, wherein an amount of the modification of the wavefront divergence is based on the eye parameters indicative of the vergence of the viewer's eyes and on an amount to correct the refractive error of the viewer's second eye; and varying an optical power of the third variable focus lens element, wherein the third variable focus lens element modifies a wavefront divergence of the incoming light from the surrounding environment, wherein an amount of the modification of the wavefront divergence is based on the eye parameters indicative of the vergence of the viewer's eyes and on an amount to correct the refractive error of the viewer's second eye.
 18. The method of claim 17, wherein determining eye parameters indicative of a vergence of the viewer's eyes comprises tracking the first and second eyes of the viewer using one or more cameras.
 19. The method of claim 16, wherein the optical power of the first variable focus lens element is varied simultaneously with the optical power of the second variable focus lens element.
 20. The method of claim 16, wherein the one or more waveguides each comprises diffractive optical elements configured to output divergent light from the waveguides. 